1. Field of the Invention
This invention generally relates to an information processing system for controlling a musical performance by using digital electronic musical instruments, and more particularly, to an interruption control apparatus used in the information processing system for controlling various interruption processes required for processing the information (hereinafter referred to as the performance information) used to play a piece of music at an appropriate timing corresponding to a specific tempo used in the performance of the piece of music.
2. Description of the Background Art
A conventional automatic system for playing a piece of music by using an information processor (hereinafter referred to as an automatic performance system) automatically renders the piece by first storing the performance information required for playing the piece of music in a storage device such as a RAM, then sequentially reading the stored performance information from the RAM, and further, converting the read information into electric signals corresponding to musical tones. In this case, the process of sequentially reading the information for playing a piece of music is synchronized with the process of incrementing the content of a register used for controlling tempo of the performance of a piece of music (hereunder referred to as a tempo register), which is incremented at a rate corresponding to the tempo selected by a player or user of the automatic performance system for playing the piece of music. Further, the content of the tempo register is incremented upon each periodic interruption of a sequencer, which is a modular component of the automatic performance system, by adding one (1) there to.
FIG. 1 (A) is a graph showing the relationship between a regular interval between one interruption and the next, and the tempo of the performance of a piece of music, when using the conventional automatic performance system. As described above, the time interval between successive interruptions (hereunder referred to as the time interval) is set in the apparatus in such a manner that it corresponds to the tempo selected by the user. Further, the tempo (i.e., the speed at which a piece of music is performed) is indicated by a number of beats per minute, and therefore, if the time interval is selected to be, for example, (1/96) times the length of a time corresponding to a quarter-note, and simultaneously, the tempo is selected to be as slow as 50 beats, each corresponding to a quarter-note per minute, the time interval has a relatively large value, given as follows: EQU 60[seconds (sec)]/(50.times.96)=12.5[milliseconds (msec)].
Conversely, if the tempo is selected to be as fast as 400 beats, each corresponding to a quarter-note per minute, the time interval has a relatively small value, determined as follows: EQU 60[seconds (sec)]/(400.times.96)=1.56[milliseconds (msec)].
Accordingly, when an 8-bit or 16-bit general-purpose central processing unit (CPU) is used in conventional electronic musical instruments such as a sequencer, it usually takes approximately 1 to 4 (msec) to effect a key assigning process, a tablet assigning process, and so on. Particularly, if another process is effected, while data recorded on a plurality of tracks is accessed by the sequencer, it will often take more than 5 msec to effect the above process.
Therefore, from the point of view of the capability of the existing general-purpose CPU, an appropriate time interval between successive interruptions of a general purpose CPU included in the sequencer should be within 3 (msec) to 6 (msec). If the period of the interruption is shorter than such an appropriate value, the process exceeds the capability of the CPU, and conversely, if the period is longer, the capability of the CPU cannot be effectively utilized, resulting in a loss of the utility of circuits of the electronic musical instruments. The present invention has been created to eliminate the above described drawback of the prior art.